Cleaning and manufacturing methods for silicon wafers, as well as methods for assessing and managing hydrogen peroxide concentration in cleaning solutions.

Abstract

This invention relates to a method for cleaning silicon wafers, characterized by roughening the silicon wafers as follows: A survey silicon wafer without a natural oxide film, exposing the bonding surface, is cleaned using a cleaning solution containing ammonium hydroxide and hydrogen peroxide at a concentration of 0–0.15 wt%. The relationship between the roughening amount on the front and back sides or the reverse side during cleaning and the cleaning temperature, NH4OH concentration, and H2O2 concentration is investigated beforehand. Based on this relationship, and according to the desired roughening amount, roughening cleaning conditions of cleaning temperature, NH4OH concentration, and H2O2 concentration are determined. Using these determined roughening cleaning conditions, the roughened target silicon wafer without a natural oxide film, exposing the bonding surface, is cleaned to roughen both sides or the reverse side. Therefore, the following technologies can be provided: a cleaning method capable of roughening the front and back sides or the reverse side of a silicon wafer; a silicon wafer manufacturing method capable of obtaining a silicon wafer with selective roughening of only one side; and an evaluation method and a management method capable of evaluating or managing trace amounts of hydrogen peroxide concentration in the cleaning solution that affect the roughening behavior.

Description

Technical Field

[0001] This invention relates to a cleaning method and manufacturing method for silicon wafers, as well as a method for evaluating and managing the hydrogen peroxide concentration in the cleaning solution. The cleaning method for silicon wafers can roughen the front and back sides or the reverse side of the silicon wafer. Prior Technology

[0002] The manufacturing process of silicon wafers for semiconductor devices may consist of the following steps: a single crystal manufacturing step of growing a single crystal rod using the Czochralski method (CZ method); a wafer processing step of slicing the single crystal rod and processing it into a mirror shape; furthermore, in order to increase added value, a tempering step of heat treatment and an epitaxial growth step of forming an epitaxial layer may be included.

[0003] The mirror-finishing process includes a DSP (double-sided polishing) step followed by a CMP (single-sided polishing) step. More specifically, from the perspective of particle quality and handling, wafers processed by DSP can be transferred to the CMP step while still in water after cleaning, without drying. Therefore, in the CMP step, a robot or similar device is used to grip and transfer the water-soaked wafers to the CMP apparatus. Furthermore, after CMP processing, wafers wetted by polishing agents and pure water are similarly gripped and transferred to the cleaning step as needed.

[0004] In this wafer processing step, wafers need to be handled in a wet environment rather than a dry environment. However, especially in this wet environment, when trying to detach the wafer held by the clamp, there are instances where the wafer cannot be detached even after the clamp is released, leading to poor handling. The reason for this is believed to be the influence of the surface roughness of the wafer to be clamped. It is argued that if the surface roughness of the wafer to be clamped is too good, the contact area with the clamp will increase, making the wafer difficult to detach even after the clamp is released. Conversely, if the surface roughness of the wafer is poor, the contact area will decrease, making the wafer easier to detach. Generally, the surface of the clamped wafer is prone to clamp marks, resulting in quality degradation; therefore, the clamping surface is mostly the reverse side of the silicon wafer. Therefore, from the viewpoint of reducing handling defects, there is a particular need for a wafer manufacturing method that can roughen only the reverse side of the silicon wafer.

[0005] A common cleaning method for silicon wafers is RCA cleaning. RCA cleaning involves cleaning with a combination of SC1 (Standard Cleaning 1), SC2 (Standard Cleaning 2), and DHF (Diluted Hydrofluoric Acid). The so-called SC1 cleaning is a cleaning method that mixes ammonia and hydrogen peroxide in any proportion and uses the alkaline cleaning solution to etch the silicon wafer surface, thereby lifting off attached particles. Furthermore, the electrostatic repulsion between the silicon wafer and the particles prevents re-adhesion and removes the particles. SC2 cleaning is a cleaning method that uses a cleaning solution made by mixing hydrochloric acid and hydrogen peroxide in any proportion to dissolve and remove metallic impurities from the silicon wafer surface. DHF cleaning is a cleaning method that uses diluted hydrofluoric acid to remove the chemical oxide film on the silicon wafer surface. Sometimes, ozone water cleaning with strong oxidizing power is also used to remove organic matter still attached to the silicon wafer surface and the chemical oxide film formed on the silicon wafer surface after DHF cleaning. Silicon wafer cleaning can be performed by combining these cleaning methods according to the desired effect. Of these, SC1 is a wash that accompanies etching, and it is generally known that SC1 wash will increase the surface roughness of the wafer.

[0006] Furthermore, as a means of evaluating wafer surface roughness, the haze value can be used as an indicator. This haze value is obtained using the Sa (three-dimensional calculated average height) value obtained by AFM (Atomic Force Microscopy) and a particle counter. Haze, which represents the so-called foginess, is widely used as an indicator of silicon surface roughness, and a higher haze level indicates a rougher wafer surface. Haze inspection using a particle counter offers very high throughput and can inspect the entire wafer surface.

[0007] Patent document 1 describes a method that uses a diluted aqueous solution to wash a silicon wafer to form a natural oxide film of varying thickness. The diluted aqueous solution contains ammonium hydroxide, hydrogen peroxide, and water in the range of 1:1:5 to 1:1:2000. Patent document 2 states that during SC1 cleaning, if the concentration of OH- separated by ammonium hydroxide electrolysis is high, it will preferentially trigger the direct etching of Si, and the surface roughness of the wafer will increase. In addition, patent documents 3 to 6 also disclose techniques for cleaning semiconductor substrates such as silicon wafers.

[0008] Furthermore, the concentrations of ammonium hydroxide and hydrogen peroxide in SC1 cleaning solution decrease due to decomposition and evaporation reactions, especially when used at high temperatures. Therefore, it is desirable to monitor and maintain a constant concentration of the liquid reagent. While concentration determination using absorbance and refractive index is known to be highly accurate, its concentration range remains somewhat limited. In particular, assessing low concentrations of the liquid reagent is currently difficult. [Previous Technical Documents] (Patent Documents)

[0009] Patent document 1: Japanese Patent Application Publication No. 7-66195. Patent document 2: Japanese Patent Application Publication No. 2011-82372. Patent document 3: Japanese Patent Application Publication No. 7-240394. Patent document 4: Japanese Patent Application Publication No. 10-242107. Patent document 5: Japanese Patent Application Publication No. 11-121419. Patent document 6: Japanese Patent Publication No. 2012-523706. Summary of the Invention

[0010] [The problem the invention aims to solve] As mentioned above, in order to reduce handling defects during processing, a silicon wafer with a rough back side is required for clamping. This invention addresses the above-mentioned problem by providing the following technologies: a cleaning method capable of roughening both sides of a silicon wafer; a silicon wafer manufacturing method capable of obtaining silicon wafers with selective roughening of only one side; and an evaluation method and a management method capable of evaluating or managing trace amounts of hydrogen peroxide concentration in the cleaning solution that affect roughening behavior. [Technical means to solve the problem]

[0011] To achieve the above objectives, the present invention provides a method for cleaning silicon wafers, characterized by roughening the silicon wafers and comprising the following steps: The cleaning solution concentration investigation step involves obtaining, beforehand, the correlation between the roughening amount of the front and back sides of the roughened silicon wafer and the temperature of the cleaning solution, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide in the cleaning solution. The roughened silicon wafer is formed by roughening the silicon wafer without a natural oxide film and with exposed bonding surfaces by cleaning it with the cleaning solution, which contains ammonium hydroxide and is an aqueous solution with a hydrogen peroxide concentration of 0~0.15wt%. The roughening cleaning condition determination step is based on the aforementioned correlation obtained in the cleaning solution concentration investigation step, and determines the roughening cleaning conditions, including the temperature of the cleaning solution, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide, according to the desired roughening amount; and, The roughening cleaning step utilizes the roughening cleaning conditions determined in the roughening cleaning condition determination step to roughen the front and back sides or the reverse side of the roughening target silicon wafer by cleaning the exposed bonding surface without a natural oxide film.

[0012] By using this silicon wafer cleaning method, a silicon wafer can be manufactured by roughening its front and back sides or reverse sides with a desired roughening amount. Furthermore, by investigating the dependence of hydrogen peroxide concentration on the roughening amount, more suitable roughening cleaning conditions can be selected. In particular, roughening cleaning conditions can be selected in a way that minimizes the variation in the roughening amount.

[0013] At this time, in the aforementioned cleaning solution concentration investigation step, the Haze value can be obtained by using a particle counter before and after the aforementioned cleaning of the aforementioned silicon wafer used for investigation, and the increase in the Haze value after the aforementioned cleaning is set as the aforementioned roughening amount.

[0014] By following this method, it is possible to easily and efficiently monitor roughening behavior and the amount of roughening.

[0015] Furthermore, when determining the aforementioned roughening cleaning conditions in the aforementioned roughening cleaning condition determination step, the aforementioned roughening cleaning conditions can be determined in the following manner: The aforementioned hydrogen peroxide concentration is within a concentration range where the change in the aforementioned roughening amount is below a specific value relative to the change in the hydrogen peroxide concentration, and on the surface of the aforementioned roughened silicon wafer after the aforementioned roughening cleaning step, there is a natural oxide film formed during the cleaning process.

[0016] By using this method, even if the concentration of hydrogen peroxide in the cleaning solution changes, the wafers roughened to the desired roughening amount can still be stably supplied. Furthermore, wafers with a more sufficient degree of roughening can be obtained.

[0017] Furthermore, in the aforementioned step of determining the roughening and cleaning conditions, the temperature of the cleaning solution can be set to 80°C or higher.

[0018] By following this method, it is possible to further reduce the variation in roughening amount relative to the variation in hydrogen peroxide concentration, and to further stabilize the supply to the roughened wafer.

[0019] Furthermore, the present invention provides a method for manufacturing a silicon wafer, characterized in that a silicon wafer is obtained by cleaning the silicon wafer by the cleaning method of the present invention, performing CMP processing on one side of the roughened silicon wafer, and selectively roughening only on the side opposite to the aforementioned side.

[0020] Thus, by grinding only one side after roughening both sides, it is possible to produce a wafer with one side in good condition and selectively roughening only the side opposite to that side.

[0021] Furthermore, the present invention provides a method for manufacturing a silicon wafer, characterized in that a silicon wafer is obtained by cleaning the silicon wafer using the cleaning method of the present invention, and roughening is performed by cleaning only the back side using a single-wafer method.

[0022] This allows the production of a wafer that is roughened only by cleaning the back side.

[0023] Furthermore, the present invention provides a method for evaluating the hydrogen peroxide concentration in a cleaning solution, characterized by comprising the following steps: The cleaning solution concentration investigation step involves obtaining, beforehand, the correlation between the roughening amount of the front and back sides of the roughened silicon wafer under investigation and the temperature of the cleaning solution, the concentration of ammonium hydroxide in the aforementioned cleaning solution, and the concentration of hydrogen peroxide in the aforementioned cleaning solution. The roughened silicon wafer under investigation has a natural oxide film and is roughened by cleaning with the aforementioned cleaning solution, which contains ammonium hydroxide and is an aqueous solution with a hydrogen peroxide concentration of 0-0.15 wt%. The hydrogen peroxide concentration assessment step is based on the aforementioned correlation obtained in the cleaning solution concentration investigation step. The hydrogen peroxide concentration in the cleaning solution is assessed according to the roughening amount of the front and back sides of the roughened silicon wafer, the temperature of the cleaning solution of the assessment object, and the concentration of ammonium hydroxide in the aforementioned cleaning solution of the assessment object. The roughened silicon wafer is formed by roughening a silicon wafer with a natural oxide film by cleaning it with the aforementioned cleaning solution of the assessment object. The cleaning solution of the assessment object is an aqueous solution containing at least ammonium hydroxide.

[0024] Any method for assessing the hydrogen peroxide concentration in a cleaning solution can accurately assess the trace amounts of hydrogen peroxide that affect roughening behavior.

[0025] Furthermore, the present invention provides a method for managing the hydrogen peroxide concentration in a cleaning solution, characterized in that the hydrogen peroxide concentration in the cleaning solution of the aforementioned assessment object is assessed using the hydrogen peroxide concentration assessment method of the present invention. The concentration of hydrogen peroxide in the cleaning solution after the evaluation is adjusted based on the evaluation results.

[0026] As long as it is a method for managing the hydrogen peroxide concentration in the cleaning solution, the hydrogen peroxide concentration can be managed with good precision and the roughening process can be carried out stably. [The effects of the invention]

[0027] Any silicon wafer cleaning method of the present invention can roughen the front and back sides or the reverse side of a silicon wafer. Furthermore, any silicon wafer manufacturing method of the present invention can produce a wafer in which one side is in good condition and is selectively roughened only on the side opposite to that side. Furthermore, as long as it is the method and management method for assessing and managing the hydrogen peroxide concentration in the cleaning solution of the present invention, it is possible to accurately assess and manage the trace amounts of hydrogen peroxide concentration in the cleaning solution used for roughening cleaning. Simple Explanation of the Diagram

[0028] Figure 1 is a flowchart illustrating an example of the cleaning method for silicon wafers according to the present invention. Figure 2 shows the relationship between the increase in haze, the number of LLS, and the surface condition of the silicon wafer at the junction surface after cleaning with various liquid compositions, as well as SEM images of level 5 and level 9. Figure 3 is a graph showing the increase in haze relative to the concentration of H2O2 at three different NH4OH concentration levels when the temperature of the cleaning solution is 80°C. Figure 4 is a graph showing the increase in Haze relative to the concentration of H₂O₂ when the temperature of the cleaning solution is 45°C or 60°C. Figure 5 shows the increase in haze relative to the washing time after washing with a washing solution containing 0.03 wt% NH4OH and 0.05 wt% H2O2 at a washing temperature of 80°C. Figure 6 is a flowchart illustrating an example of the method for assessing and managing the concentration of hydrogen peroxide in the cleaning solution of the present invention. Figure 7 is a graph showing the increase in Haze relative to the concentration of H2O2 when the washing temperature is 80°C and the NH4OH concentration is 0.03wt%, and it is also a graph showing the results (correlation) of the washing solution concentration investigation step of S11 in the example. Figure 8 is a graph showing the increase in Haze relative to the H2O2 concentration when the washing temperature is 80°C and the NH4OH concentration is at two different levels, and it is also a graph showing the results (correlation) of the washing solution concentration investigation step of S1 in the example. Implementation

[0029] The present invention will now be described in detail with reference to drawings as an example of an embodiment, but the present invention is not limited thereto. First, the method and mechanism of the roughening phenomenon in this invention are described. Figure 2 shows a wafer with exposed bonding surfaces and after DSP cleaning (marked as levels 1 to 12) by changing the composition of SC1 (liquid composition NH4OH:H2O2:H2O), cleaning temperature, and cleaning time. The roughness index, or Haze value, is obtained using a particle counter, and the difference between this value and the Haze value obtained before cleaning is displayed. The increase in the Haze value after cleaning (hereinafter also referred to as the Haze increase) is an example of the roughening amount. A higher value indicates a rougher surface. The surface observation results of the unroughened Ref (standard) and levels 5 and 9 using SEM (Scanning Electron Microscopy) are also shown.

[0030] The liquid reagents used are 28% by mass ammonia (NH4OH) and 30% by mass hydrogen peroxide (H2O2), which are also indicated by mass (wt). Furthermore, the mass % is the concentration of the cleaning solution as a percentage of the mass ratio of the solute (ammonium hydroxide, hydrogen peroxide) it contains, and can also be indicated by wt%.

[0031] It can be seen that the Haze value increases significantly at levels 5, 6, 8, 9, and 12. Further observation of the SEM images reveals unevenness at levels 5 and 9, while this unevenness is not observed in the standard sample. From the above analysis, it can be concluded that the surface exhibits significant roughness at these levels, indicating that roughening has been performed. On the other hand, in levels 3, 4, and 11, the increase was approximately 0.8–0.9 ppm, which is too small to be considered as roughening. Furthermore, the number of LLS (Localized Light Scatter) was also very high, and the defect quality deteriorated significantly. The fact that the surface after cleaning is hydrophobic suggests that the bonding surfaces are exposed during cleaning, and Si etching occurs significantly, forming etching pits. In other levels, the surface is hydrophilic, but the increase in haze is also slight.

[0032] The roughening mechanism is described in detail. During SC1 cleaning, hydrogen peroxide acts as an oxidant, oxidizing Si to form SiO2 (a natural oxide film, hereinafter also referred to as an oxide film). Ammonium hydroxide releases OH- through ionization, which etches the SiO2 on the wafer surface. In typical liquid cleaning solutions (e.g., NH4OH:H2O2:H2O = 1:1:10), an oxide film is often present on the wafer during cleaning, while the interface (Si) is not exposed, and the thickness of the formed oxide film is often around 1 nm, independent of cleaning time. This is known to be due to the balance between oxidation and etching rates. That is, in liquid cleaning solutions with a certain concentration or higher of H2O2, the oxidation rate of Si generated by H2O2 is faster than the etching rate of SiO2 generated by OH-, thus explaining why Si is not exposed and why an oxide film is often present on the wafer. In other words, if the concentration of H₂O₂ is below a certain level, the etching rate generated by OH⁻ will be faster than the oxidation rate of Si generated by H₂O₂. Therefore, the oxidation cannot keep up, and the etching reaction of Si generated by OH⁻ will take place. In this case, Si will be exposed after cleaning and thus become a water-repellent surface.

[0033] It can be seen that the composition of the liquid reagent at this roughening level, for example, is similar to level 5 with NH4OH:H2O2:H2O = 1:0.4:1000, where the H2O2 ratio is lower than that of NH4OH. Therefore, it is believed that if such a liquid reagent is used to clean the silicon wafer at the interface, the cleaned surface will be hydrophilic, so an initial oxidation reaction will occur to form an oxide film. However, the oxidation rate is relatively slow, thus the etching of SiO2 will be relatively advantageous. SiO2 will be etched, and Si will be etched at the points where Si is locally exposed, thereby achieving roughening.

[0034] Thus, the roughening phenomenon of the present invention is a phenomenon that occurs within a balance between the oxidation reaction and the etching reaction. Furthermore, in order to ensure stable roughening, it is necessary to perform cleaning using a liquid composition and liquid reagent concentration that are stable for these reactions.

[0035] Based on the above, the cleaning method of the present invention will be described. Figure 1 is a flowchart illustrating an example of the cleaning method for silicon wafers according to the present invention. (Step S1: Cleaning solution concentration investigation) In S1 of Figure 1, a cleaning solution concentration investigation step is performed as a preliminary test to select the roughening cleaning conditions that can stably carry out the roughening phenomenon. That is, it is a step in which the relationship between the roughening amount and the temperature of the cleaning solution, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide in the cleaning solution are obtained in advance. Here, the so-called roughening amount refers to the roughening amount of the front and back sides (or the reverse side) of the silicon wafer under investigation (without a natural oxide film and with the junction surface exposed) by cleaning it with a cleaning solution (an aqueous solution containing ammonium hydroxide and with a hydrogen peroxide concentration of 0~0.15wt%). For example, it can be set as the aforementioned haze increase. As long as it is the haze increase, the roughening behavior and roughening amount can be monitored easily and efficiently, which is better. Furthermore, as an example of the cleaning solution mentioned above, when the hydrogen peroxide concentration is set to 0 wt%, it can be set as an aqueous solution containing ammonium hydroxide. In addition, if the hydrogen peroxide concentration is not 0 wt%, it can be set as an aqueous solution containing ammonium hydroxide and hydrogen peroxide water.

[0036] The following provides more specific examples to illustrate the steps for investigating the concentration of the cleaning solution. Figure 3 shows the increase in haze before and after cleaning a silicon wafer without a natural oxide film on its interface at 80°C for 3 minutes. The cleaning was performed by varying the H₂O₂ concentration at three levels of NH₄OH: 0.03, 0.13, and 0.25 wt%. The surface condition after cleaning (○ for the 0.03 wt% NH₄OH concentration, ● for the hydrophilic surface) is also shown.

[0037] For example, considering an NH₄OH concentration of 0.03 wt%, the increase in haze varies depending on the H₂O₂ concentration. The increase in haze is smaller at H₂O₂ concentrations of 0 wt% and 0.007 wt%. This is because if the H₂O₂ concentration is too low, the oxidation rate becomes too slow, and only etching of the Si occurs. This is consistent with the case where the surface after cleaning with only a low concentration of H₂O₂ is a water-repellent surface (with the bonded Si surface exposed). As mentioned earlier, in the case of a hydrophobic surface, Si etching becomes significant and LLS quality (LLS quantity) deteriorates. Therefore, it is desirable to perform roughening within the range of becoming a hydrophilic surface. At H₂O₂ concentrations of 0.019 wt% to 0.078 wt%, the surface state is hydrophilic with a significant increase in haze, and roughening was performed. Subsequently, below 0.09 wt%, although it is still a hydrophilic surface, the increase in haze decreases. This is because the H₂O₂ concentration is too high, causing the Si oxidation rate to become significantly faster than the etching rate, and the etching effect to become relatively weaker.

[0038] Furthermore, this cleaning concentration investigation step is preferably carried out using multiple levels of NH4OH concentration and cleaning temperature. As shown in the figure, the increase in haze becomes greater at higher NH4OH concentrations. Therefore, when setting the desired increase in haze (deterioration) in step S2 described later, having multiple levels of investigation results makes it easier to select rougher cleaning conditions.

[0039] Furthermore, the inventors' investigation revealed that when the H₂O₂ concentration is greater than 0.15 wt%, even if the NH₄OH concentration is increased to a high level within a practical range, the oxidation rate will still increase without causing roughening. Therefore, in step S1, as mentioned above, the H₂O₂ concentration is below 0~0.15 wt%.

[0040] (Step S2: The roughening and cleaning conditions determine the steps) Subsequently, based on the results of S1, the roughening cleaning condition determination step of S2 is implemented. That is, it is a step that, based on the correlation of S1, determines the roughening cleaning conditions of the cleaning solution temperature, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide in the cleaning solution by the desired roughening amount (haze increase). Furthermore, the value of the expected increase in Haze can be determined according to its extent.

[0041] In this step, the particular aim is to select roughening cleaning conditions that exhibit stability in relation to changes in H₂O₂ concentration, based on the correlation obtained in S1. Figure 3 shows that when the NH4OH concentration is 0.03 wt%, the increase in haze is relatively stable within the range of 0.032 to 0.078 wt%. At this point, for example, by setting the H2O2 concentration to 0.05 wt%, even if the H2O2 concentration in the cleaning solution changes unexpectedly, the change in haze increase is still relatively small and stable compared to that change. Therefore, it will not deviate significantly from the desired haze increase, and roughening can be achieved more stably with the desired haze increase. Thus, the H2O2 concentration chosen as one of the roughening cleaning conditions is preferably determined from a range below the value (desired value) where the change in haze increase is relatively small compared to the change in H2O2 concentration. This specific value can be appropriately set from a value greater than 0, depending on the required accuracy, etc.

[0042] Subsequently, considering the NH4OH concentrations of 0.13 wt% and 0.25 wt%, the slower oxidation rate at lower H2O2 concentrations becomes an etching advantage, leading to significant variations in haze increase and indicating instability. Therefore, roughening is not desired within this range. Since higher NH4OH concentrations result in faster etching rates, it is assumed that the variation would exceed 0.03 wt%. However, it is known that if the H₂O₂ concentration increases, the increase in haze will exhibit a stable range of H₂O₂ concentration, similar to the case of 0.03 wt%. If the NH₄OH concentration is different, the required range of H₂O₂ concentration to stabilize the increase in haze will also change. Therefore, by pre-determining an appropriate range of H₂O₂ concentration, the roughening process can be carried out more stably.

[0043] Furthermore, considering that a higher NH4OH concentration results in a greater increase in haze, the desired roughness (haze increase) can be achieved by adjusting the NH4OH concentration. For example, to obtain a wafer with a haze increase of 5 ppm, the following roughening cleaning conditions can be selected: NH4OH concentration set to 0.03 wt% and H2O2 concentration set to 0.05 wt%, with cleaning at 80°C for 3 minutes. On the other hand, to obtain a wafer with a haze increase of 30 ppm, the following roughening cleaning conditions can be selected: NH4OH concentration set to 0.25 wt% and H2O2 concentration set to 0.07 wt%, with cleaning at 80°C for 3 minutes. By thus anticipating the variation in haze increase relative to H2O2 concentration, roughening cleaning conditions that ensure more stable roughening can be selected.

[0044] Furthermore, in step S2, as long as the roughening cleaning conditions are determined by the amount of natural oxide film residue formed during the cleaning in S3 on the roughened silicon wafer surface after cleaning, the degree of roughening can be further improved, which is preferable. A hydrophilic surface can also be obtained, and the degradation of LLS quantity can be prevented.

[0045] Next, the influence of the temperature of the cleaning solution (cleaning temperature) will be described. Figure 4 shows the variation in haze increase when washing at 45°C and 60°C with NH₄OH concentrations of 0.03 wt% and 0.25 wt% and a washing time of 3 minutes. While the haze increase is still the largest condition across all three levels, compared to Figure 3 at 80°C, the range of stable H₂O₂ concentrations for haze increase is narrower, as previously mentioned. This suggests that choosing between a washing temperature above 80°C and either the washing solution concentration investigation step (S1) or the roughening washing condition determination step (S2) allows for a more stable roughening washing condition. This is attributed to the stable oxidation effect of hydrogen peroxide at higher temperatures. There is no specific upper limit to the washing temperature; for example, 90°C is acceptable.

[0046] However, it is not necessary to be 80°C or above. There are also areas where the increase in haze will be greater below 60°C, so roughening can still be carried out. For example, by shortening the life of the liquid agent, the variation in the increase in haze caused by the change in the concentration of H2O2 in the cleaning solution can also be suppressed.

[0047] Next, the impact of washing time will be described. Figure 5 shows the increase in haze when washing with a washing solution containing 0.03 wt% NH4OH and 0.05 wt% H2O2 at a washing temperature of 80°C for washing times of 30, 60, 180, and 360 seconds. It can be seen that the longer the washing time, the greater the increase in haze. Therefore, in addition to the NH4OH concentration, H2O2 concentration, and washing temperature, the degree of roughening can be further adjusted by changing the washing time. The degree of roughening can be controlled by adjusting the NH4OH concentration or the washing time, as described above, as long as it is used appropriately according to the needs. This also allows for further consideration of the relationship between washing time and the conditions for roughening washing in S2.

[0048] (Step S3: Roughening and Cleaning Step) Subsequently, in the roughening and cleaning step S3, the silicon wafer without a natural oxide film on the bonding surface is cleaned under the roughening and cleaning conditions determined in S2. This cleaning process roughens both sides (or the reverse side) of the silicon wafer. Thus, by performing step S3 through the aforementioned S1 and S2, a roughened wafer with the desired increase in haze can be reliably obtained. Furthermore, it avoids significant deviations from the desired increase in haze (i.e., the variation in haze increase is small), and can be fabricated with a stable degree of roughness.

[0049] Next, the cleaning method for implementing the present invention will be described. Currently, most wafer cleaning methods utilize liquids such as liquid agents and pure water, and are thus called wet cleaning. Among these methods, the main types can be divided into batch cleaning, which cleans a large number of wafers at once, and single-wafer cleaning, which processes individual wafers one by one. In batch cleaning, both the front and back sides of the wafer are immersed in liquid agents in the device configuration; therefore, if the cleaning method of the present invention is implemented, both sides will be roughened. In contrast, in single-wafer cleaning, the liquid agent is sprayed while the wafer is rotated, so only one side of the wafer can be cleaned. According to the inventors' research, the present invention can achieve roughening using either the batch or single-wafer method. An appropriate method can be selected by considering the wafer manufacturing steps.

[0050] As mentioned above, to produce a wafer with only the back side roughened, in a single-wafer process, only the back side can be cleaned, while in a batch process, both the front and back sides can be roughened simultaneously. Therefore, in the silicon wafer manufacturing method of the present invention, it is desirable that after cleaning by the cleaning method of the present invention, the quality of the front side is particularly improved by the polishing step. For example, by using a batch cleaning machine to perform the wafer cleaning method of the present invention, both sides of the silicon wafer are roughened at the same time, and then one side (i.e., the front side) is subjected to single-sided grinding such as CMP grinding, thereby producing a wafer that selectively roughens only the side opposite to that side (i.e., the back side). As long as the wafer is of this type, it will not cause gripping defects even in a wet environment, and can be manufactured stably.

[0051] Next, regarding the cleaning solution used for roughening in the aforementioned cleaning method of the present invention, a method for assessing and managing the hydrogen peroxide concentration in the cleaning solution will be described. As described above, since the roughening behavior of this invention is strongly dependent on the hydrogen peroxide concentration, managing the hydrogen peroxide concentration allows for more stable roughening. As a method for evaluating the liquid agent concentration of a typical SC1 cleaning solution, a concentration determination method using absorbance and refractive index is available, and its high accuracy is known. However, when the inventors attempted to perform roughening cleaning, for example, by using absorbance to measure the concentration of a cleaning solution prepared with 0.25 wt% NH4OH and 0.07 wt% H2O2, although the NH4OH concentration was detected as 0.24 wt%, the H2O2 concentration was below the detection limit and therefore undetectable.

[0052] Therefore, the inventors utilized the aforementioned roughening behavior to address the inability to assess and manage H₂O₂ concentration. Figure 6 shows the flow chart of the method for assessing and managing hydrogen peroxide concentration in the cleaning solution of this invention. (Step S11: Cleaning solution concentration investigation) The initial investigation procedure, similar to that of S11, is as follows: For the silicon wafer (with a natural oxide film) used in the investigation, the correlation between the roughening amount (e.g., the increase in haze) and the temperature of the cleaning solution (an aqueous solution containing ammonium hydroxide and hydrogen peroxide at a concentration of 0~0.15 wt%), as well as the concentration of ammonium hydroxide and hydrogen peroxide in the cleaning solution, is obtained in advance. Furthermore, as an example of the cleaning solution mentioned above, when the hydrogen peroxide concentration is 0 wt%, it can be set as an aqueous solution containing ammonium hydroxide. In addition, if the hydrogen peroxide concentration is not 0 wt%, it can be set as an aqueous solution containing ammonium hydroxide and hydrogen peroxide water (SC1 cleaning solution).

[0053] Here, unlike the cleaning solution concentration investigation step S1 in the aforementioned silicon wafer cleaning method of the present invention (using silicon wafers without a natural oxide film as the investigation material), the reason for using wafers with a natural oxide film in the cleaning solution concentration investigation step S11 of the hydrogen peroxide concentration evaluation method in the cleaning solution of the present invention is as follows. In cleaning methods, it is particularly important to seek a region where the variation in roughness relative to the amount of hydrogen peroxide is small and stable. Although a method without a natural oxide film can still achieve a tendency as shown in Figure 3, in such cases, it becomes impossible to obtain the hydrogen peroxide concentration corresponding to the amount of roughness without discrepancy. On the other hand, when a natural oxide film is present, as will be discussed later, the higher the hydrogen peroxide concentration, the more likely the roughness will decrease, thus allowing the hydrogen peroxide concentration to be determined without discrepancy from the amount of roughness.

[0054] The following provides more specific examples to illustrate the steps for investigating the concentration of the cleaning solution. First, a silicon wafer with a natural oxide film was prepared for investigation. In order to calculate the increase in haze, the haze value was obtained using a particle counter before cleaning. Furthermore, as methods for forming a natural oxide film, general methods include SC1 washing and ozone water washing. These washing methods are not particularly limited as long as a natural oxide film can be formed after washing. Preferably, the mixing ratio (volume ratio) of the SC1 washing solution is, for example, NH4OH:H2O2:H2O = 1:1:10, the temperature is 30~80℃, and the washing time is 90~360 seconds. Preferably, the concentration of ozone water is in the range of 3~25 ppm, the temperature is 10~30℃, and the washing time is 60~360 seconds.

[0055] Subsequently, the aforementioned cleaning solutions were prepared at various temperatures, and the concentrations of NH4OH and H2O2 were varied (and the cleaning time was also varied as needed). The silicon wafers with natural oxide films were cleaned to roughen the front and back sides (or the back side), and the Haze value was obtained using a particle counter. Figure 7 shows the increase in haze relative to the H₂O₂ concentration when the washing temperature is 80°C, the washing time is 3 minutes, and the NH₄OH concentration in the washing solution is 0.03 wt%. Unlike the trend observed at the interface (e.g., Figure 3), it is evident that the higher the H₂O₂ concentration, the smaller the increase in haze. Thus, the correlation between washing temperature, NH₄OH concentration, H₂O₂ concentration, and haze increase was obtained beforehand. Furthermore, the inventors' research showed that when the H₂O₂ concentration is greater than 0.15 wt%, the increase in haze becomes approximately zero, making it unsuitable as an indicator. On the other hand, this invention is an evaluation method for cleaning solutions with an H₂O₂ concentration of less than 0.15 wt%, which can accurately assess the H₂O₂ concentration even in such minute quantities.

[0056] (Step S12: Hydrogen peroxide concentration assessment procedure) Next, similar to the hydrogen peroxide concentration assessment step in S12, using the cleaning solution (containing at least an aqueous solution of ammonium hydroxide) of the target material for which the H₂O₂ concentration is to be measured, the silicon wafer, which also has a natural oxide film as in S11, is cleaned at the specific cleaning temperature (and further, a specific cleaning time) obtained in the correlation obtained in S11 to obtain the increase in haze. Furthermore, the NH₄OH concentration can be determined and calculated, for example, using conventional methods. In particular, if the washing temperature (and washing time) are set in advance, steps S11 and S12 can be performed easily at the same washing temperature. Subsequently, based on the correlation obtained in S11, the H2O2 concentration can be evaluated according to the increase in Haze, washing temperature (and washing time), and NH4OH concentration obtained above.

[0057] (Step S13: Hydrogen peroxide concentration management procedure) Furthermore, similar to the hydrogen peroxide concentration management step in step S13, the hydrogen peroxide concentration in the cleaning solution can be adjusted based on the evaluation results obtained in S12. For example, after initially using a cleaning solution prepared with an NH₄OH concentration of 0.03 wt% and an H₂O₂ concentration of 0.05 wt% for a specific period of time, when evaluating the H₂O₂ concentration using the evaluation method of the present invention, if the concentration is determined to be 0.04 wt%, hydrogen peroxide water can be added to make the H₂O₂ concentration 0.05 wt%. Conversely, if the concentration is determined to be 0.06 wt%, pure water can be added to make the H₂O₂ concentration 0.05 wt%. By implementing such a management method, the liquid reagent lifespan can be extended, and a roughened wafer with a stable increase in halogen content can be manufactured. This operation allows for precise assessment and even management of trace amounts of H₂O₂ concentration, such as 0–0.15 wt%, in the cleaning solution, thereby enabling the stable production of the desired roughened wafers. [Example]

[0058] The present invention will be further described below based on embodiments, but these embodiments are illustrative and not intended to be limiting. (Example 1) As shown in Figure 1 of the cleaning method of the present invention, the cleaning solution concentration investigation step of S1, which is a preliminary test, is carried out in advance. Using a particle counter SP3 manufactured by KLA Corporation, the haze value of silicon wafers (survey wafers) without a natural oxide film on the bonding surface after DSP processing was obtained. Subsequently, using 28% by mass ammonia (NH4OH) and, as needed, 30% by mass hydrogen peroxide (H2O2), two cleaning solutions with NH4OH concentrations of 0.03 wt% and 0.25 wt% were prepared at a cleaning temperature of 80°C. The H2O2 concentration was varied within the range of 0–0.15 wt%, and the silicon wafers on the bonding surface were cleaned for 3 minutes. The haze value was then obtained using SP3, and the increase in haze was calculated from the difference before and after cleaning. Figure 8 shows the correlation between the increase in Haze, the concentration of NH4OH, and the concentration of H2O2 at a washing temperature of 80°C.

[0059] Next, the roughening and cleaning conditions determination step of S2 is implemented. The objective is to produce wafers with two levels of haze increase: 10 ppm and 30 ppm. The roughening cleaning conditions for achieving these haze increase levels are determined based on the correlation in Figure 8 derived in S1. For a 10 ppm halogen concentration, considering an NH₄OH concentration of 0.03 wt%, it can be seen that the halogen increase remains relatively stable at approximately 5-6 ppm when the H₂O₂ concentration is in the range of approximately 0.03-0.08 wt%. Therefore, in the subsequent S3 step, for the cleaning solution used on the roughened silicon wafer, the NH₄OH concentration is set to 0.03 wt%, the H₂O₂ concentration is set to 0.05 wt% (within the 0.03-0.08 wt%), and the cleaning temperature is set to 80°C. Regarding cleaning time, the halogen increase is positively correlated with the cleaning time. Based on a halogen increase of 5-6 ppm at 3 minutes, the cleaning time is set to twice 3 minutes, i.e., 6 minutes. With this setting, an halogen increase of approximately 10 ppm is expected.

[0060] Regarding the 30 ppm halogen concentration, considering an NH₄OH concentration of 0.25 wt%, it can be seen that within the H₂O₂ concentration range of 0.05–0.09 wt%, the halogen increase stabilizes at approximately 30 ppm. Based on this, for the washing solution, the NH₄OH concentration was set to 0.25 wt%, the H₂O₂ concentration to 0.07 wt% within the 0.05–0.09 wt% range, and the washing temperature to 80°C. The washing time, which corresponds to the 30 ppm halogen increase at 3 minutes, was also set to 3 minutes, similar to the case in S1.

[0061] Next, the roughening and cleaning step S3 is performed. Using two roughening cleaning conditions with target haze increases of 10 ppm and 30 ppm determined in S2, a batch cleaning machine was used to clean silicon wafers (the roughening target silicon wafers) without a natural oxide film on the bonding surface after DSP processing (5 wafers of each level) to roughen both sides. Haze values ​​were obtained using SP3 to calculate the haze increase. The average haze increase for wafers with a target of 10 ppm was 10.7 ppm, and the average haze increase for wafers with a target of 30 ppm was 31.2 ppm, thus enabling the production of wafers with roughness equivalent to the target haze increase. Furthermore, the LLS quality was 1 pc on wafers with a target of 10 ppm and 0 pcs on wafers with a target of 30 ppm, which is considered good.

[0062] For wafers with target haze increases of 10 ppm and 30 ppm respectively, obtained by double-sided roughening using this method, CMP processing with a machining allowance of 500 nm was performed on their surface sides. When the LLS count of each CMP-processed wafer was evaluated using an SP5 / 19nmUP manufactured by KLA Corporation, it was 12 pcs for a target of 10 ppm and 9 pcs for a target of 30 ppm, exhibiting the same and good quality as Comparative Example 1 described later. Subsequently, when the handling test was repeated 200 times, no adverse results were achieved in both levels. The handling test involved clamping the back side of each wafer stored in water and unchucking the wafer onto the stage of the grinding machine.

[0063] (Example 2) Subsequently, based on the evaluation method of the present invention shown in Figure 6, the concentration of hydrogen peroxide in the cleaning solution used to stably perform roughening cleaning is evaluated. With the amount of Haze increased to 10 ppm, the hydrogen peroxide concentration of the washing solution was evaluated based on the results of S2 and S3 in Example 1, when the concentration of NH4OH was 0.03 wt%, the concentration of H2O2 was 0.05 wt%, and the temperature was 80°C. Initially, following the same procedure as S11 for investigating the concentration of the cleaning solution, the correlation between cleaning temperature (80°C), NH4OH concentration (0.03 wt%), H2O2 concentration, and roughening amount was obtained. Specifically, firstly, silicon wafers were cleaned at 80°C for 3 minutes using a cleaning solution of NH4OH:H2O2:H2O = 1:1:10 to create wafers with a native oxide film (the silicon wafers used in the investigation). The haze value was obtained using SP3. Then, the H2O2 concentration was varied in a cleaning solution with an NH4OH concentration of 0.03 wt% and a cleaning temperature of 80°C to clean the silicon wafers with the native oxide film for 3 minutes. The haze value of the cleaned wafers was obtained using SP3, and the increase in haze was calculated. The results are the same as in Figure 7. That is, the haze value was 41 ppm when the H2O2 concentration was 0.05 wt% and 181 ppm when it was 0.02 wt%, demonstrating a correlation that the roughness (i.e., the increase in haze) decreases with increasing H2O2 concentration.

[0064] Subsequently, the hydrogen peroxide concentration assessment procedure of S12 was implemented. First, 200 silicon wafers were cleaned using the cleaning solution to produce double-sided roughened silicon wafers. To evaluate the hydrogen peroxide concentration in the cleaning solution (the evaluation cleaning solution) after cleaning the 200 wafers, the haze value was obtained using SP3 after cleaning wafers with a pre-determined haze value and a native oxide film, and the haze increase was calculated. The result showed a haze increase of 60 ppm. Referring to the relevant relationships in Figure 7, the H₂O₂ concentration in the cleaning solution of the evaluated object is approximately 0.04 wt%. Considering that the target H₂O₂ concentration before cleaning 200 wafers was 0.05 wt%, the concentration decrease is estimated to be approximately 0.01 wt%. This is likely due to the effects of liquid reagent adhering to the wafers and the pure water (rinsing) tank after cleaning 200 wafers.

[0065] Then, using the hydrogen peroxide concentration management step of S13, H2O2 is added to the cleaning solution to achieve the target H2O2 concentration of 0.05 wt%. Subsequently, to confirm this, after cleaning the wafer with the native oxide film where the haze value had already been obtained, the haze value was obtained using SP3 and the increase in haze was calculated. The result was 40 ppm, and based on the correlation, the H 2O 2 concentration was calculated to be approximately 0.05 wt%, confirming that the H 2O 2 concentration was as expected.

[0066] The results above show that by using the cleaning method of the present invention, the front and back sides (especially the back side) of the silicon wafer can be sufficiently roughened to exhibit a roughness suitable for adsorption by clamping. Furthermore, by using the hydrogen peroxide concentration assessment and management method in the cleaning solution of the present invention, it is possible to assess and even manage trace amounts of hydrogen peroxide concentration, which was previously difficult.

[0067] (Comparative Example) Silicon wafers without a natural oxide film on the bonding surface after DSP processing were prepared, and haze evaluation was performed using SP3. Subsequently, a batch cleaning machine was used to perform cleaning under the six levels of conditions (liquid composition, cleaning temperature, and cleaning time) shown in Table 1. The cleaning solution consisted of 28% by mass ammonia (NH4OH) and 30% by mass hydrogen peroxide (H2O2). The cleaned wafers were evaluated using SP3 to obtain haze values ​​and calculate the increase in haze.

[0068] In all levels in Table 1, the increase in haze was less than 1 ppm. Considering that it was less than 10 ppm and 30 ppm in Example 1, it was determined that it was not roughened. After CMP processing with a machining allowance of 500nm on wafers of Levels 1 and 5, the LLS (Limited Latency Sinking) count was evaluated using SP5 / 19nmUP. The count was 10 pcs in Level 1 and 342 pcs in Level 5. It was concluded that although the LLS level in Level 1 was the same as in Example 1, the etching pits formed during the roughening and cleaning step in Level 5 would remain in the CMP step, thus degrading the LLS quality. Subsequently, 200 clamping tests, identical to those in Example 1, were performed on wafers of Levels 1 and 5. The defect of wafers failing to detach from the clamp occurred 4 times in Level 1 and 3 times in Level 5. In addition, the concentration of H2O2 in the cleaning solution at level 5 was detected using a concentration meter based on absorbance, but it was below the detection limit and could not be evaluated.

[0069] [Table 1] level NH 4OH [wt%] H₂O₂ [wt%] Washing temperature [℃] Washing time [minute] Haze increase [ppm] 1 2.1 2.8 45℃ 3 minutes 0.03 2 2.1 2.8 60℃ 3 minutes 0.07 3 2.1 2.8 80℃ 3 minutes 0.12 4 0.25 0.33 80℃ 3 minutes 0.23 5 0.03 0.007 80℃ 3 minutes 0.7 6 0.03 0.1 80℃ 3 minutes -0.7

[0070] Furthermore, this invention is not limited to the embodiments described above. The embodiments described above are examples; any embodiments that have substantially the same structure and can perform the same function as the technical concept described in the claims of this invention are included within the technical scope of this invention.

[0071] none

[0072] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method for cleaning a silicon wafer, characterized by roughening the silicon wafer and comprising the following steps: a cleaning solution concentration investigation step, wherein the roughening amount of the front and back sides of the roughened silicon wafer for investigation is obtained in advance, and the relationship between the temperature of the cleaning solution, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide in the cleaning solution is obtained. The roughened silicon wafer for investigation is formed by roughening a silicon wafer for investigation without a natural oxide film and exposed bonding surfaces by cleaning it with a cleaning solution containing ammonium hydroxide and being an aqueous solution with a hydrogen peroxide concentration of 0 to 0.15 wt%; a roughening cleaning condition determination step, wherein the roughening cleaning conditions, namely the temperature of the cleaning solution, the concentration of ammonium hydroxide in the cleaning solution, and the concentration of hydrogen peroxide, are determined based on the aforementioned relationship obtained in advance in the cleaning solution concentration investigation step, according to the desired roughening amount; and, The roughening cleaning step utilizes the roughening cleaning conditions determined in the roughening cleaning condition determination step to roughen the front and back sides or the reverse side of the roughening target silicon wafer by cleaning the exposed bonding surface without a natural oxide film.

2. The cleaning method for silicon wafers as described in claim 1, wherein, In the aforementioned cleaning solution concentration investigation step, the Haze value is obtained using a particle counter before and after the aforementioned cleaning of the silicon wafer used for investigation, and the increase in the Haze value after the aforementioned cleaning is set as the aforementioned roughening amount.

3. The cleaning method for silicon wafers as described in claim 1, wherein, When determining the roughening cleaning conditions in the aforementioned roughening cleaning condition determination step, the aforementioned roughening cleaning conditions are determined in the following manner: the aforementioned hydrogen peroxide concentration is within a concentration range where the change in the aforementioned roughening amount is below a specific value relative to the change in the hydrogen peroxide concentration, and on the surface of the roughened silicon wafer after the aforementioned roughening cleaning step, there is a natural oxide film formed during the cleaning.

4. The cleaning method for silicon wafers as described in claim 2, wherein, When determining the roughening cleaning conditions in the aforementioned roughening cleaning condition determination step, the aforementioned roughening cleaning conditions are determined in the following manner: the aforementioned hydrogen peroxide concentration is within a concentration range where the change in the aforementioned roughening amount is below a specific value relative to the change in the hydrogen peroxide concentration, and on the surface of the roughened silicon wafer after the aforementioned roughening cleaning step, there is a natural oxide film formed during the cleaning.

5. A cleaning method for silicon wafers as described in any one of claims 1 to 4, wherein, In the aforementioned step of determining the roughening and cleaning conditions, the temperature of the cleaning solution is set to 80°C or higher.

6. A method for manufacturing a silicon wafer, characterized in that a silicon wafer is obtained by cleaning it using the silicon wafer cleaning method described in any one of claims 1 to 5, performing CMP processing on one side of the roughened silicon wafer, and selectively roughening only on the side opposite to the aforementioned side.

7. A method for manufacturing a silicon wafer, characterized in that a silicon wafer is obtained by cleaning it using the silicon wafer cleaning method described in any one of claims 1 to 5, and roughening is performed by cleaning only the back side using a single-wafer method.

8. A method for assessing the hydrogen peroxide concentration in a cleaning solution, characterized by comprising the following steps: a cleaning solution concentration investigation step, wherein the correlation between the roughening amount of the front and back sides or the reverse side of a roughened silicon wafer for investigation and the temperature of the cleaning solution, the concentration of ammonium hydroxide in the aforementioned cleaning solution, and the concentration of hydrogen peroxide in the aforementioned cleaning solution is obtained in advance, wherein the roughened silicon wafer for investigation has a natural oxide film and is roughened by cleaning with the aforementioned cleaning solution, the cleaning solution containing ammonium hydroxide and being an aqueous solution with a hydrogen peroxide concentration of 0 to 0.15 wt%; and, The hydrogen peroxide concentration assessment step is based on the aforementioned correlation obtained in the cleaning solution concentration investigation step. The hydrogen peroxide concentration in the cleaning solution is assessed according to the roughening amount of the front and back sides of the roughened silicon wafer, the temperature of the cleaning solution of the assessment object, and the concentration of ammonium hydroxide in the aforementioned cleaning solution of the assessment object. The roughened silicon wafer is formed by roughening a silicon wafer with a natural oxide film by cleaning it with the aforementioned cleaning solution of the assessment object. The cleaning solution of the assessment object is an aqueous solution containing at least ammonium hydroxide.

9. A method for managing the hydrogen peroxide concentration in a cleaning solution, characterized in that the hydrogen peroxide concentration in the cleaning solution of the aforementioned assessment object is assessed by the hydrogen peroxide concentration assessment method in claim 8, and the hydrogen peroxide concentration in the assessed cleaning solution is adjusted based on the assessment result.

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